The primary aim of the proposed work is to study the transport mechanism of levodopa and its derivatives across brain tissues and renal tubules. Research work done in this laboratory has shown that there are structural and stereospecificities in renal tubular transport of Levodopa. The efflux of levodopa from CSF to blood is also a carrier- mediated transport process. Simultaneous stationary microperfusion of Proximal tubule and perfusion of peritubular capillaries shows that there is a bi-directional transport process for levodopa with reabsorption predominating over secretion. The rate of transport of levodopa is significantly reduced b metabolic inhibitor but not by decarboxylase inhibitor. The study of the time course of metabolism of levodopa shows that the transport process is independent from the metabolism of this compound. Ventricular perfusion experiments have shown that the major metabolite, 3,4-dihydroxyphenlacetic acid is transported from CSF to blood by a system different from that of levodopa. We plan to determine the structural requirements of levodopa transport in brain tissues and the correlation between this system and the transport system in the renal tubule. Cellular distribution of levodopa and its derivatives will be pursued by autoradiographic techniques.